Underfill compounds including electrically charged filler elements, microelectronic devices having underfill compounds including electrically charged filler elements, and methods of underfilling microelectronic devices

ABSTRACT

Underfill compounds including electrically charged filler elements, microelectronic devices having underfill compounds including electrically charged filler elements, and methods of disposing underfill including electrically charged filler elements on microelectronic devices are disclosed herein. In one embodiment, a microelectronic device includes a microelectronic component, a plurality of electrical couplers carried by the microelectronic component, and an underfill layer covering at least a portion of the electrical couplers. The underfill layer comprises a binder and a plurality of electrically charged filler elements in the binder. The underfill layer can include a first zone having a first concentration of electrically charged filler elements and a second zone having a second concentration of electrically charged filler elements different than the first concentration.

TECHNICAL FIELD

The present invention relates to underfll compounds includingelectrically charged filler elements, microelectronic devices havingunderfill compounds including electrically charged filler elements, andmethods of disposing underfill compounds having electrically chargedfiller elements on microelectronic devices.

BACKGROUND

Microelectronic device assemblies, such as memory devices andmicroprocessors, typically include one or more microelectroniccomponents attached to a substrate, The microelectronic componentscommonly, include at least one die having functional features such asmemory cells, integrated circuits, and interconnecting circuitry. Thedies of the microelectronic components may be encased in a plastic,ceramic, or metal protective covering. Each die commonly includes anarray of very small bond-pads electrically coupled to the functionalfeatures. The bond-pads can be used to operatively connect themicroelectronic component to the substrate.

One type of microelectronic component is a “flip-chip” semiconductordevice. These components are referred to as “flip-chips” because theyare typically manufactured on a wafer and have an active side withbond-pads that initially face upward. After manufacture is completed anda die is singulated, the die is inverted or “flipped” such that theactive side bearing the bond-pads faces downward for attachment to asubstrate. The bond-pads are usually coupled to terminals, such asconductive “bumps,” that electrically and mechanically connect the dieto the substrate. The bumps on the flip-chip can be formed from solders,conductive polymers, or other materials. In applications using solderbumps, the solder bumps are reflowed to form a solder joint between theflip-chip component and the substrate. This leaves a small gap betweenthe flip-chip and the substrate. To enhance the integrity of the jointbetween the microelectronic component and the substrate, an underfillmaterial is introduced into the gap. The underfill material bears someof the stress placed on the components and protects the components frommoisture, chemicals and other contaminants. The underfill material caninclude filler particles to increase the rigidity of the material andmodify the coefficient of thermal expansion of the material.

The underfill material typically is dispensed into the underfill gap bydepositing a bead of the underfill material along one or two sides ofthe flip-chip when the underfill material is in a fluidic state (i.e.,flowable). As shown schematically in FIG. 1, a bead of an underfillmaterial U may be dispensed along one side of the die D. The flowableunderfill material will then be drawn into the gap between the die D andthe substrate S by capillary action. The direction of this movement isindicated by the arrows in FIG. 1. After the underfill material fillsthe gap, it is cured to a hardened state. Although such a “singlestroke” process yields good results, the processing time necessary topermit the underfill material U to flow across the entire width of thedie can reduce the throughput of the manufacturing process.

FIG. 2 illustrates an alternative approach wherein the underfillmaterial U is applied in an L-shaped bead along two adjacent sides ofthe die D. By reducing the average distance that the underfill materialhas to flow to fill the underfill gap, processing times can be reduced.The L-stroke approach, however, can lead to more voids in the underfillmaterial, which adversely affect the integrity of the bond between thedie D and the substrate S.

In the single stroke and L-stroke approaches, the filler particles canbecome segregated from the polymer fluid as the underfill material flowsacross the die. Consequently, one side of the flip-chip often has agreater concentration of filler particles. The nonuniform distributionof filler particles creates differences in the rigidity and thecoefficient of thermal expansion of the underfill material across thedie.

In other embodiments, the underfill material may be deposited across aplurality of dies at the wafer-level to form an underfill layer. Afterthe underfill layer is formed, the dies can be singulated and attachedto substrates. Forming an underfill layer with filler particles on a diebefore attaching a substrate to the die has some drawbacks. For example,the filler particles in the portion of the underfill layer above theconductive bumps can obstruct the connection between the conductivebumps of the die and the substrate. To prevent the filler particles frominterfering with the connection, one approach is to form two underfilllayers on the die. The first underfill layer includes filler particlesand has a thickness no greater than the height of the conductive bumps.The second underfill layer is formed over the first layer and does notcontain filler particles. This approach, however, requires twodispensers and two types of underfill material. Another approach is toform the underfill layer on the die at the wafer-level before formingthe conductive bumps. Next, vias are formed in the underfill layer andthe conductive bumps are formed in the vias. This approach, however, iscomplicated and can result in contamination of the underfill layerand/or the conductive bumps. Moreover, it is difficult to deposit solderpaste in very small vias. Another approach is to form the underfilllayer over the die and the conductive bumps, then remove the top portionof the underfill layer so that the underfill layer has a thickness equalto the height of the conductive bumps. This approach also iscomplicated, requires cleaning, and may contaminate the device.Accordingly, a new method for forming an underfill layer that has fillerparticles is needed.

SUMMARY OF THE INVENTION

The present invention is directed to underfill compounds includingelectrically charged filler elements, microelectronic devices havingunderfill compounds including electrically charged filler elements, andmethods of disposing underfill compounds including electrically chargedfiller elements on microelectronic devices. One aspect of the inventionis directed to a composition for use in an underfill layer of amicroelectronic device. In one embodiment, the composition includes aflowable binder and a plurality of electrically charged filler elementsdisposed within the flowable binder. The electrically charged fillerelements can include silica, silicon nitride, aluminum oxide, and/oraluminum nitride. The flowable binder can include a liquid polymer.

Another aspect of the invention is directed to a microelectronic device.In one embodiment, the microelectronic device includes a microelectroniccomponent, a plurality of electrical couplers carried by themicroelectronic component, and an underfill layer covering at least aportion of the plurality of electrical couplers. The underfill layercomprises a binder and a plurality of electrically charged fillerelements in the binder. In one aspect of this embodiment, the underfilllayer also includes a first zone having a first concentration ofelectrically charged filler elements and a second zone having a secondconcentration of electrically charged filler elements different from thefirst concentration. The first zone can include the portion of theunderfill layer between the distal ends of the electrical couplers, andthe second zone can include the portion of the underfill layer betweenthe distal ends of the electrical couplers and a distal surface of theunderfill layer. Alternatively, the underfill layer can include a firstzone and a plurality of second zones. The second zones can be generallyhemispherical and extend between the distal surface of the underfilllayer and the distal ends of the electrical couplers.

Another aspect of the invention is directed to a method for disposingunderfill material on a microelectronic device having a plurality ofelectrical couplers. In one embodiment, the method includes depositingan underfill layer onto the microelectronic device and covering at leasta portion of the electrical couplers. The underfill layer includes abinder and a plurality of electrically charged filler elements in thebinder. The method further includes applying an electric field to theunderfill layer to manipulate at least a portion of the electricallycharged filler elements. In one aspect of this embodiment, applying theelectric field includes moving at least a portion of the electricallycharged filler elements from a first zone into a second zone.

Another aspect of the invention is directed to a method of underfillinga microelectronic device assembly including a microelectronic component,a substrate, and a plurality of electrical couplers coupling themicroelectronic component to the substrate. In one embodiment, themethod includes disposing an underfill layer including a plurality ofelectrically charged filler elements between the microelectroniccomponent and the substrate and moving at least a portion of theplurality of electrically charged filler elements within the underfilllayer by applying an electric field to the underfill layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a prior art underfill process.

FIG. 2 is a schematic illustration of another prior art underfillprocess.

FIGS. 3-6 illustrate various stages in a method of disposing anunderfill material on a microelectronic device and attaching the deviceto a substrate.

FIG. 3 is a schematic side cross-sectional view of a microelectronicworkpiece including a plurality of microelectronic devices afterdepositing an underfill layer.

FIG. 4A is a schematic side cross-sectional view of the microelectronicdevices after moving at least some of the electrically charged fillerelements within the underfill layer.

FIG. 4B is a schematic side cross-sectional view of a plurality ofmicroelectronic devices after moving at least some of the electricallycharged filler elements within an underfill layer in accordance withanother embodiment of the invention.

FIG. 5 is a schematic side cross-sectional view of the microelectronicdevice of FIG. 4A after singulation.

FIG. 6 is a schematic side cross-sectional view of a microelectronicdevice assembly.

FIG. 7 is a schematic side cross-sectional view of a microelectronicworkpiece having a plurality of microelectronic devices in accordancewith another embodiment of the invention.

FIGS. 8-10 illustrate various microelectronic device assemblies inaccordance with additional embodiments of the invention.

FIG. 8 is a schematic side cross-sectional view of a microelectronicdevice assembly including a microelectronic component and a substratecoupled to the microelectronic component.

FIG. 9 is a schematic side cross-sectional view of a microelectronicdevice assembly in accordance with another embodiment of the invention.

FIG. 10 is a schematic side cross-sectional view of a microelectronicdevice assembly in accordance with another embodiment of the invention.

DETAILED DESCRIPTION

The following description is directed toward microelectronic devices,microelectronic device assemblies, methods for disposing underfillmaterial on microelectronic devices, and methods for underfillingmicroelectronic device assemblies. The term “microelectronic workpiece”is used throughout to include substrates upon which and/or in whichmicroelectronic devices, micromechanical devices, data storage elements,and other features are fabricated. For example, microelectronicworkpieces can be semiconductor wafers, glass substrates, insulativesubstrates, or many other types of substrates. Many specific details ofseveral embodiments of the invention are described below with referenceto a microelectronic device including a microelectronic die in order toprovide a thorough understanding of such embodiments. Those of ordinaryskill in the art will thus understand that the invention may have otherembodiments with additional elements or without several of the elementsdescribed in this section.

FIGS. 3-6 illustrate various stages in a method of disposing anunderfill material on a microelectronic device and attaching the deviceto a substrate. In the illustrated method, an underfill material isdisposed on a plurality of microelectronic devices as part of a batchprocess. In other embodiments, the underfill material can be disposed ona single microelectronic device according to the illustrated method.

FIG. 3 is a schematic side cross-sectional view of a microelectronicworkpiece including a plurality of microelectronic devices 100(identified individually as 100 a-c) after depositing an underfill layer150 in accordance with one embodiment of the invention. Themicroelectronic devices 100 can be formed on a substrate 108, and eachdevice 100 can include a microelectronic component such as a die 110having an integrated circuit 111 (shown schematically) and a pluralityof bond-pads 112 coupled to the integrated circuit 111. Themicroelectronic devices 100 can each include a redistribution assembly120 with ball-pads 122 and traces 124 for coupling the, bond-pads 112 ofa corresponding die 110 to a printed circuit board or other device. Theball-pads 122 are arranged in ball-pad arrays relative to the dies 110such that each die 110 has a corresponding array of ball-pads 122. Theredistribution assemblies 120 can be separate components of aredistribution layer 125 that include a dielectric stratum 126separating the traces 124 and the ball-pads 122.

In the illustrated embodiment, the microelectronic devices 100 alsoinclude a plurality of electrical couplers 130, such as solder balls,formed on corresponding ball-pads 122 of the redistribution assembly120. In other embodiments, the microelectronic devices may not include aredistribution assembly. In these embodiments, the electrical couplerscan be formed directly on the bond-pads of the microelectronic dies orother types of electrical terminals coupled to the dies.

The microelectronic devices 100 of FIG. 3 include the underfill layer150 to protect the devices 100 from moisture, chemicals andcontaminants. In one aspect of the illustrated embodiment, the underfilllayer 150 has a thickness T₁ greater than the height. T₂ of theelectrical couplers 130. In other embodiments, the underfill layer 150may not cover all of the electrical couplers 130. In another aspect ofthe illustrated embodiment, the underfill layer 150 includes a flowablematrix or binder 151 and a plurality of electrically charged fillerelements 152 disposed within the binder 151. The binder 151 can includean epoxy, a resin, or suitable material. The electrically charged fillerelements 152 can be micelles including an organic substance and fillerparticles in the organic substance. The filler particles can be silica,silicon nitride, aluminum nitride, aluminum oxide, or other suitablematerials. In the illustrated embodiment, the electrically chargedfiller elements 152 have a positive charge. In other embodiments, theelectrically charged filler elements can have a negative charge. Theelectrically charged filler elements 152 increase the rigidity andmodify the coefficient of thermal expansion of the underfill layer 150.

FIG. 4A is a schematic side cross-sectional view of the microelectronicdevices 100 after moving at least some of the electrically chargedfiller elements 152 within the underfill layer 150 while the binder 151is in a flowable state. In the illustrated embodiment, each electricalcoupler 130 has a proximal end 131 coupled to a corresponding ball-pad122 and a distal end 132 opposite the proximal end 131. The distal ends132 of the electrical couplers 130 define a plane P₁ that divides theunderfill layer 150 into a first zone Z₁ and a second zone Z₂. The firstzone Z₁ includes the portion of the underfill layer 150 between theplane P₁ and the redistribution layer 125, and the second zone Z₂includes the portion of the underfill layer 150 between the plane P₁ anda surface 153 of the underfill layer 150.

In one aspect of the illustrated embodiment, an electric field source160, such as a charged plate, selectively generates an electric field tomove the electrically charged filler elements 152 within the underfilllayer 150. For example, the electric field source 160 can repel theelectrically charged filler elements 152 causing at least some of theelements 152 to move from the second zone Z₂ to the first zone Z₁.Accordingly, the concentration of electrically charged filler elements152 in the second zone Z₂ is less than the concentration of electricallycharged filler elements 152 in the first zone Z₁. Removing theelectrically charged filler elements 152 from the second zone Z₂ of theunderfill 150 allows the electrical couplers 130 to be properly andreliably connected to another device, such as a printed circuit board,as will be described in detail below.

After the electrically charged filler elements 152 have been moved tothe first zone Z₁ of the underfill layer 150, the underfill layer 150can be partially cured, such as to a “B” stage (partially linked), toprevent the elements 152 from migrating back into the second zone Z₂.The substrate 108 of the microelectronic devices 100 can also be background to reduce the profile of the devices 100. After curing, thesubstrate 108, redistribution layer 125, and the underfill layer 150 canbe cut along lines A₁ and A₂ to singulate the microelectronic devices100.

FIG. 4B is a schematic side cross-sectional view of a plurality ofmicroelectronic devices 200 after moving at least some of theelectrically charged filler elements 152 within an underfill layer 250in accordance with another embodiment of the invention. In thisembodiment, a plurality of electric field sources 260 generate discreteelectric fields to repel the electrically charged filler elements 152from a plurality of second zones Z₄ to a first zone Z₃. The second zonesZ₄ can be generally hemispherical and can include the portion of theunderfill layer 250 between a surface 253 of the underfill layer 250 andthe distal ends 132 of the electrical couplers 130. The first zone Z₃includes the portion of the underfill layer 250 outside the second zonesZ₄. After the electrically charged filler elements 152 have moved fromthe second zones Z₄, the underfill layer 250 can be partially cured toprevent the electrically charged filler elements 152 from moving backinto the second zones Z₄. Furthermore, as described above with referenceto FIG. 4A, the microelectronic devices 200 can be back ground andsingulated.

FIG. 5 is a schematic side cross-sectional view of the microelectronicdevice 100 a of FIG. 4A after singulation. The singulatedmicroelectronic device 100 a can be attached to a substrate 370, such asa printed circuit board. The substrate 370 includes a plurality ofcontacts 372 aligned with the electrical couplers 130 of themicroelectronic device 100 a. To attach the substrate 370 to themicroelectronic device 100 a, the contacts 372 are pressed into thesecond zone Z₂ of the underfill layer 150. As discussed above, thesecond zone Z₂ of the underfill layer 150 does not include electricallycharged filler elements 152, and thus the filler elements 152 do notinterfere with the connection between the electrical couplers 130 andthe contacts 372.

FIG. 6 is a schematic side cross-sectional view of a microelectronicdevice assembly 480 including the microelectronic device 100 a attachedto the substrate 370. After the contacts 372 of the substrate 370 arepositioned against the electrical couplers 130, the microelectronicdevice assembly 480 can pass through the reflow process to melt thesolder balls 130 and to securely join the ball-pads 122 to the contacts372. Furthermore, the underfill layer 150 can be fully cured.

One advantage of the method illustrated in FIGS. 3-6 is that a fillet454 is created in the underfill 150 and 250 that increases the rigidityof the microelectronic device assembly 480. More specifically, as thecontacts 372 are pressed into the underfill 150 and 250, a portion ofthe underfill 150 and 250 is forced outward, creating the fillet 454between the substrate 370 and the microelectronic device 100.

Another advantage of the microelectronic device assembly 480 is theimproved electrical connection and mechanical bond between the contacts372 and the electrical couplers 130. In the prior art, before thesubstrate was attached to the microelectronic device, the portion of theunderfill between the contacts of the substrate and the electricalcouplers of the microelectronic device included filler particles. Whenthe substrate was attached to the microelectronic device these fillerparticles sometimes were trapped between the contacts and the electricalcouplers. Consequently, these filler particles degraded the electricalconductivity and the mechanical integrity of the connection. In themethod illustrated in FIGS. 3-6, the filler elements 152 are moved outof the portion of the underfill layer 150 and 250 between the contacts372 and the electrical couplers 130 before attachment to prevent thefiller elements 152 from becoming trapped between the contacts 372 andthe electrical couplers 130. Accordingly, the microelectronic deviceassembly 480 has an improved electrical connection and mechanical bondbetween the substrate 370 and the microelectronic device 100 a.Furthermore, with the method illustrated in FIGS. 3-6, it is notnecessary to remove a top layer of the underfill layer 150 and 250 andexpose the electrical couplers 130 in order to achieve the improvedconnection between the contacts 372 and the electrical couplers 130.Accordingly, the elimination of this planarizing step reduces themechanical stress on the electrical couplers 130 and the contaminationof the underfill layer 150 and 250.

FIG. 7 is a schematic side cross-sectional view of a microelectronicworkpiece having a plurality of microelectronic devices 500 inaccordance with another embodiment of the invention. The microelectronicdevices 500 can be similar to the microelectronic devices 100 discussedabove with reference to FIG. 3. For example, the microelectronic devices500 include an underfill layer 550 having a first zone Z₁, a second zoneZ₂, and a plurality of electrically charged filler elements 152. In theillustrated embodiment, an electric field source 560 attracts theelectrically charged filler elements 152 to move them into the secondzone Z₂ of the underfill layer 550. Next, the underfill layer 550 can beat least partially cured, and the second zone Z₂ of the underfill layer550 can be removed from the microelectronic devices 500 by planarizationor another suitable method. After the second zone Z₂ of the underfilllayer 550 is removed, the microelectronic devices 500 can be diced andattached to substrates without filler elements 152 interfering with theconnection between the contacts on the substrate and the electricalcouplers 130.

FIGS. 8-10 illustrate various microelectronic device assemblies inaccordance with additional embodiments of the invention. FIG. 8 is aschematic side cross-sectional view of a microelectronic device assembly600 including a microelectronic component 610 and a substrate 670coupled to the microelectronic component 610. The microelectroniccomponent 610 includes a plurality of ball-pads 622 coupled tocorresponding contacts 672 on the substrate 670 by electrical couplers630.

The microelectronic device assembly 600 also includes an underfill layer650 having a plurality of electrically charged filler elements 652. Theunderfill layer 650 can be applied to the microelectronic deviceassembly 600 by dispensing a bead of underfill material along one sideof the microelectronic component 610. The underfill material will thenbe drawn into the gap between the microelectronic component 610 and thesubstrate 670 by capillary action, as described above with reference toFIGS. 1 and 2. Alternatively, the underfill layer 650 can be applied tothe microelectronic device assembly 600 by the method described abovewith reference to FIGS. 3-6. In one aspect of the illustratedembodiment, the electrically charged filler elements 652 have the samecharge and consequently repel each other. Accordingly, the electricallycharged filler elements 652 disperse throughout the underfill layer 650,creating a generally uniform distribution of the elements 652. Thegenerally uniform distribution of electrically charged filler elements652 provides a generally uniform coefficient of thermal expansion acrossthe microelectronic device assembly 600.

FIG. 9 is a schematic cross-sectional side view of a microelectronicdevice assembly 700 in accordance with another embodiment of theinvention. The microelectronic device assembly 700 is generally similarto the microelectronic device assembly 600 described above withreference to FIG. 8. For example, the microelectronic device assembly700 includes a microelectronic component 610, a substrate 670 coupled tothe microelectronic component 610, and an underfill layer 750 having aplurality of electrically charged filler elements 652 disposed betweenthe microelectronic component 610 and the substrate 670. In one aspectof the illustrated embodiment, a plane P₂ generally equidistant from themicroelectronic component 610 and the substrate 670 divides theunderfill layer 750 into a first zone Z₅ and a second zone ₆. In otherembodiments, the plane P₂ may not be equidistant from themicroelectronic component 610 and the substrate 670. In the illustratedembodiment, an electric field source 760 repels the electrically chargedfiller elements 652, and consequently moves the filler elements 652 intothe second zone Z₆. The greater concentration of the electricallycharged filler elements 652 in the second zone Z₆ reduces thecoefficient of thermal expansion of the second zone Z₆. Accordingly, thecoefficient of thermal expansion of the second zone Z₆ s less than thecoefficient of thermal expansion of the first zone Z₅.

FIG. 10 is a schematic side cross-sectional view of a microelectronicdevice assembly 800 in accordance with another embodiment of theinvention. The microelectronic device assembly 800 is generally similarto the microelectronic device assembly 600 described above withreference to FIG. 8. For example, the microelectronic device assembly800 includes a microelectronic component 610, a substrate 670 coupled tothe microelectronic component 610, and an underfill layer 850 having aplurality of electrically charged filler elements 652 disposed betweenthe microelectronic component 610 and the substrate 670. In one aspectof the illustrated embodiment, the electric field source 860 attractsthe electrically charged filler elements 652 and consequently moves thefiller elements 652 into a first zone Z₇. The greater concentration ofthe electrically charged filler elements 652 in the first zone Z₇reduces the coefficient of thermal expansion of the first zone Z₇.Accordingly, the coefficient of thermal expansion of the first zone Z₇is less than the coefficient of thermal expansion of a second zone Z₈.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

We claim:
 1. A microelectronic device, comprising: a microelectroniccomponent having an integrated circuit and bond-pads coupled to theintegrated circuit; a plurality of electrical couplers coupled to thebond-pads of the microelectronic component; and an underfill layercovering at least a portion of the plurality of electrical couplers,wherein the underfill comprises a binder and a plurality of electricallycharged filler elements in the binder.
 2. The microelectronic device ofclaim 1 wherein the electrically charged filler elements comprisesilica.
 3. The microelectronic device of claim 1 wherein the underfilllayer includes a first zone having a first concentration of electricallycharged filler elements and a second zone having a second concentrationof electrically charged filler elements different than the firstconcentration.
 4. The microelectronic device of claim 1 wherein theunderfill layer includes a first zone having a first concentration ofelectrically charged filler elements and a second zone having a secondconcentration of electrically charged filler elements different than thefirst concentration, and wherein the binder is at least partially curedbinder.
 5. The microelectronic device of claim 1 wherein the electricalcouplers include a proximal end proximate to the microelectroniccomponent and a distal end opposite the proximal end, wherein the distalends of the electrical couplers define a plane that divides theunderfill layer into a first zone between the plane and themicroelectronic component and a second zone opposite the first zone, andwherein the first zone has a first concentration of electrically chargedfiller elements and the second zone has a second concentration ofelectrically charged filler elements less than the first concentration.6. The microelectronic device of claim 1 wherein the electrical couplersinclude a proximal end proximate to the microelectronic component and adistal end opposite the proximal end, wherein the distal ends of theelectrical couplers define a plane that divides the underfill layer intoa first zone between the plane and the microelectronic component and asecond zone opposite the first zone, and wherein the first zone has afirst concentration of electrically charged filler elements and thesecond zone has a second concentration of electrically charged fillerelements greater than the first concentration.
 7. The microelectronicdevice of claim 1 wherein the electrical couplers include a proximal endproximate to the microelectronic component and a distal end opposite theproximal end, wherein underfill layer further includes a first surfaceproximate to the microelectronic component, a second surface oppositethe first surface, a first zone having a first concentration ofelectrically charged filler elements, and a second zone having a secondconcentration of electrically charged filler elements less than thefirst concentration, wherein the second zone is generally hemisphericaland extends between the second surface and the distal end of one of theelectrical couplers.
 8. The microelectronic device of claim 1 whereinthe electrical couplers comprise solder balls electrically coupled tothe microelectronic component.
 9. The microelectronic device of claim 1wherein the microelectronic component comprises a microelectronic die.10. A microelectronic workpiece, comprising: a plurality ofmicroelectronic components; a plurality of electrical couplers arrangedin discrete arrays that are electrically coupled to correspondingmicroelectronic components; and an underfill layer over at least aportion of the plurality of electrical couplers, wherein the underfilllayer comprises a binder and a plurality of electrically charged fillerelements in the binder, and wherein the underfill layer includes a firstzone having a first concentration of the electrically charged fillerelements and a second zone having a second concentration of electricallycharged filler elements different than the first concentration.
 11. Themicroelectronic workpiece of claim 10 wherein the electrically chargedfiller elements comprise silica.
 12. The microelectronic workpiece ofclaim 10 wherein the binder is at least partially cured.
 13. Themicroelectronic workpiece of claim 10 wherein the electrical couplersinclude a proximal end proximate to the microelectronic component and adistal end opposite the proximal end, wherein the distal ends of theelectrical couplers define a plane that divides the underfill layer intothe first zone between the plane and the microelectronic component andthe second zone opposite the first zone, and wherein the firstconcentration of electrically charged filler elements is less than thesecond concentration of electrically charged filler elements.
 14. Themicroelectronic workpiece of claim 10 wherein the electrical couplersinclude a proximal end proximate to the microelectronic component and adistal end opposite the proximal end, wherein the distal ends of theelectrical couplers define a plane that divides the underfill layer intothe first zone between the plane and the microelectronic component andthe second zone opposite the first zone, and wherein the firstconcentration of electrically charged filler elements is greater thanthe second concentration of electrically charged filler elements. 15.The microelectronic workpiece of claim 10 wherein the electricalcouplers include a proximal end proximate to the microelectroniccomponent and a distal end opposite the proximal end, wherein underfilllayer further includes a first surface proximate to the microelectroniccomponent and a second surface opposite the first surface, and whereinthe second zone is generally hemispherical and extends between thesecond surface and the distal end of one of the electrical couplers. 16.The microelectronic workpiece of claim 10 wherein the microelectroniccomponents comprise microelectronic dies.
 17. A microelectronic deviceassembly, comprising: a microelectronic component having an integratedcircuit and bond-pads coupled to the integrated circuit; a plurality ofelectrical couplers coupled to the bond-pads of the microelectroniccomponent; a substrate having contacts that are coupled to correspondingelectrical couplers; and an underfill layer between the microelectroniccomponent and the substrate, wherein the underfill comprises a binderand a plurality of electrically charged filler elements in the binder.18. The assembly of claim 17 wherein the electrically charged fillerelements comprise silica.
 19. The assembly of claim 17 wherein theelectrically charged filler elements are distributed generally uniformlythroughout the underfill layer.
 20. The assembly of claim 17 wherein theunderfill layer includes a first zone having a first concentration ofelectrically charged filler elements and a second zone having a secondconcentration of electrically charged filler elements different than thefirst concentration.
 21. The assembly of claim 17 wherein a planedivides the underfill layer into a first zone having a firstconcentration of electrically charged filler elements and a second zonehaving a second concentration of electrically charged filler elementsless than the first concentration, wherein the plane is generallyparallel to the microelectronic component and is between themicroelectronic component and the substrate, and wherein the first zoneincludes the portion of the underfill layer between the plane and themicroelectronic component and the second zone includes the portion ofthe underfill layer between the plane and the substrate.
 22. Theassembly of claim 17 wherein a plane divides the underfill layer into afirst zone having a first concentration of electrically charged fillerelements and a second zone having a second concentration of electricallycharged filler elements greater than the first concentration, whereinthe plane is generally parallel to the microelectronic component and isbetween the microelectronic component and the substrate, and wherein thefirst zone includes the portion of the underfill layer between the planeand the microelectronic component and the second zone includes theportion of the underfill layer between the plane and the substrate. 23.The assembly of claim 17 wherein a plane divides the underfill layerinto a first zone having a first coefficient of thermal expansion and asecond zone having a second coefficient of thermal expansion greaterthan the first coefficient, wherein the plane is generally parallel tothe microelectronic component and is between the microelectroniccomponent and the substrate, and wherein the first zone includes theportion of the underfill layer between the plane and the microelectroniccomponent and the second zone includes the portion of the underfilllayer between the plane and the substrate.
 24. The assembly of claim 17wherein a plane divides the underfill layer into a first zone having afirst coefficient of thermal expansion and a second zone having a secondcoefficient of thermal expansion less than the first coefficient,wherein the plane is generally parallel to the microelectronic componentand is between the microelectronic component and the substrate, andwherein the first zone includes the portion of the underfill layerbetween the plane and the microelectronic component and the second zoneincludes the portion of the underfill layer between the plane and thesubstrate.
 25. The assembly of claim 17 wherein the electrical couplerscomprise solder balls electrically coupled to the microelectroniccomponent.
 26. The assembly of claim 17 wherein the microelectroniccomponent comprises a microelectronic die.
 27. A microelectronic deviceassembly, comprising: a microelectronic component having a plurality ofpads; a plurality of electrical couplers electrically coupled tocorresponding pads; a substrate having contacts that are coupled tocorresponding electrical couplers; and an underfill layer between themicroelectronic component and the substrate, wherein the underfillcomprises a binder and a plurality of electrically charged fillerelements in the binder, and wherein the plurality of electricallycharged filler elements are distributed generally uniformly throughoutthe underfill.
 28. The assembly of claim 27 wherein the electricallycharged filler elements comprise silica.
 29. The assembly of claim 27wherein the electrical couplers comprise solder balls.
 30. The assemblyof claim 27 wherein the microelectronic component comprises amicroelectronic die.
 31. A microelectronic device assembly, comprising:a microelectronic component having a plurality of pads; a plurality ofelectrical couplers electrically coupled to the plurality of pads; asubstrate having contacts that are coupled to the electrical couplers;and an underfill layer between the microelectronic component and thesubstrate, wherein the underfill comprises a binder and a plurality ofelectrically charged filler elements in the binder, and wherein theunderfill layer includes a first zone having a first concentration ofelectrically charged filler elements and a second zone having a secondconcentration of electrically charged filler elements different than thefirst concentration.
 32. The assembly of claim 31 wherein theelectrically charged filler elements comprise silica.
 33. The assemblyof claim 31 wherein a plane divides the underfill layer into the firstzone and the second zone, wherein the plane is generally parallel to themicroelectronic component and is between the microelectronic componentand the substrate, wherein the first zone includes the portion of theunderfill layer between the plane and the microelectronic component andthe second zone includes the portion of the underfill layer between theplane and the substrate, and wherein the first concentration ofelectrically charged filler elements is greater than the secondconcentration.
 34. The assembly of claim 31 wherein a plane divides theunderfill layer into the first zone and the second zone, wherein theplane is generally parallel to the microelectronic component and isbetween the microelectronic component and the substrate, wherein thefirst zone includes the portion of the underfill layer between the planeand the microelectronic component and the second zone includes theportion of the underfill layer between the plane and the substrate, andwherein the first concentration of electrically charged filler elementsis less than the second concentration.
 35. The assembly of claim 31wherein a plane divides the underfill layer into the first zone and thesecond zone, wherein the plane is generally parallel to themicroelectronic component and is between the microelectronic componentand the substrate, wherein the first zone includes the portion of theunderfill layer between the plane and the microelectronic component andthe second zone includes the portion of the underfill layer between theplane and the substrate, and wherein the first zone has a firstcoefficient of thermal expansion and the second zone has a secondcoefficient of thermal expansion less than the first coefficient. 36.The assembly of claim 31 wherein a plane divides the underfill layerinto the first zone and the second zone, wherein the plane is generallyparallel to the microelectronic component and is between themicroelectronic component and the substrate, wherein the first zoneincludes the portion of the underfill layer between the plane and themicroelectronic component and the second zone includes the portion ofthe underfill layer between the plane and the substrate, and wherein thefirst zone has a first coefficient of thermal expansion and the secondzone has a second coefficient of thermal expansion greater than thefirst coefficient.
 37. A composition for use in an underfill layer of amicroelectronic device, comprising: a flowable binder having a firststate in which the binder is flowable and a second state with a greaterviscosity than the first state; and a plurality of electrically chargedfiller elements disposed within the flowable binder.
 38. The compositionof claim 37 wherein the electrically charged filler elements comprisesilica.
 39. The composition of claim 37 wherein the electrically chargedfiller elements comprise silicon nitride.
 40. The composition of claim37 wherein the electrically charged filler elements comprise aluminumoxide.
 41. The composition of claim 37 wherein the electrically chargedfiller elements comprise aluminum nitride.
 42. The composition of claim37 wherein the flowable binder comprises a liquid polymer.